Parsnips: fiber, folate and a sap that burns in sunlight

The best evidence about parsnips is not about nutrition. In a randomized crossover feeding study, 36 healthy adults aged 20 to 40 ate four fully controlled six-day diets in random order, and the diet built on the parsnip family lowered CYP1A2 activity (P of 0.02 or below) while the cabbage family raised it (P below 0.04), with no change in NAT2 or xanthine oxidase. CYP1A2 is the enzyme that clears caffeine and a list of medicines. The abstract never says which vegetables made up that diet, so the finding belongs to the family parsnip sits in and not to parsnip as such. A second randomized crossover, in 25 adults, did name it. Parsnip, fresh parsley and celery sticks eaten with a well-done burger shifted the 660 urinary metabolites measured far less than cabbage-family vegetables did, mainly raising mannitol and sorbitol. Neither trial measured a clinical outcome, so this is metabolism, not benefit.

The numbers, per 3.5 oz (100 g)

As people eat it, per 3.5 oz (100 g)

How much is actually in it

• Iron in raw parsnip varies more than fourfold between samples, from 0.302 to 1.38 mg per 3.5 oz (100 g), and folate varies by half. — 8 Foundation Foods samples of Parsnips, raw (FDC 2747659) (n = 8) Evidence E source
  Iron mean 0.5053 mg/100 g, range 0.302 to 1.38, spread 213 percent; folate mean 83.42 microgram, range 65.72 to 106.3, spread 49 percent; fiber mean 5.351 g, spread 26 percent
• US and UK food tables agree on parsnip folate and fiber within about a tenth, but differ on vitamin C by 30 percent, 11.85 against 17 mg per 3.5 oz (100 g). — reference entries for raw parsnip in two national composition tables (n = 2 dataset entries) Evidence E source
  Vitamin C USDA 11.85 vs CoFID 17 mg/100 g (30 percent apart); folate 83.42 vs 87 microgram (4 percent); fiber 5.351 vs 4.7 g (12 percent)
• Parsnip root carries about 26.8 g of dietary fiber per 3.5 oz (100 g) of dry matter and 1.3 g of fructans, at 47 calories per 3.5 oz (100 g) fresh. — published compositional analyses of Pastinaca sativa root collected in a 2026 review Evidence D source
  21 g/100 g organic matter, 26.8 g/100 g dry matter dietary fiber, 1.3 g/100 g dry matter fructans, 5.9 g/100 g dry matter crude protein, 47 calories per 3.5 oz (100 g)

What a real portion looks like

• US survey coding puts a cup of cooked parsnip at 160 g and one whole parsnip at 100 g. — US dietary survey portion coding for cooked parsnips (n = 2 dataset entries) Evidence E source
  1 cup cooked = 160 g; 1 whole = 100 g

What your body absorbs

• Six days of a diet built on the parsnip family lowered CYP1A2 activity in 36 adults, while cabbage-family vegetables raised it, in a randomized crossover feeding study. — 19 men and 17 women aged 20 to 40, non-smokers on no medication, four 6-day fully controlled diets in random order: vegetable-free basal, brassica, allium and apiaceous (n = 36) Evidence B source
  CYP1A2 activity differed by diet at P of 0.0005 or below; apiaceous vegetables lowered it at P of 0.02 or below and brassica raised it at P below 0.04; no effect on NAT2 or xanthine oxidase
• Adding parsnip, parsley and celery to a well-done burger shifted urinary metabolites far less than adding cabbage-family vegetables, in a randomized crossover trial in 25 adults. — 25 adults, randomized crossover with four phases, each ending in one of four test meals: well-done hamburger alone, plus apiaceous vegetables (parsnip, fresh parsley and celery sticks), plus cruciferous vegetables, or plus both (n = 25) Evidence B source
  660 urinary metabolites measured; the combined vegetable meal changed 133 of them versus control; the apiaceous meal mainly raised mannitol and sorbitol and barely moved xenobiotic metabolites

What cooking and storage change

• Boiling root vegetables in a little water and draining leaves 70 percent of the vitamin C and 70 percent of the folate, while the minerals stay at 90 to 95 percent. — USDA retention factors for the group Vegetables and Vegetable Products, method VEG,ROOTS,ETC,BLD,DRAIND,LITTLE WTR Evidence E source
  Vitamin C 70 percent retained, folate 70 percent, thiamin 85 percent, phosphorus and potassium 90 percent, calcium iron magnesium zinc copper riboflavin niacin and vitamin B6 95 percent
• Holding parsnip through a 30 day post-harvest aging process raised its total phenolic content roughly tenfold, from 0.0089 to 0.0897 mg GAE per ml of extract. — parsnip root aged 10, 20 and 30 days after harvest, compared with raw parsnip and red ginseng, three replicates (n = 3 replicates per group) Evidence D source
  Total phenolics 0.0089 mg/ml GAE raw, 0.0449 at 10 days, 0.0849 at 20 days, 0.0897 at 30 days (P < 0.01 versus raw); DPPH scavenging rose in parallel

What it does to your health

• In mice, an aged parsnip extract at a dose the authors equate to about 10 g of fresh parsnip for a 154 lb (70 kg) adult lowered lung TNF-alpha and IL-1beta after an irritant challenge. — C57BL/6J mice given 10 mg of aged parsnip extract per kg body weight orally for 2 weeks before intranasal acrolein Evidence D source
  TNF-alpha and IL-1beta mRNA down versus the challenged control (P < 0.001 and P < 0.05); serum GM-CSF, IL-23, IL-6, ICAM-1, IL-17 and IFN-gamma also reduced

Safety, limits and interactions

• Parsnip is dominated by furanocoumarins, which cause phytophotodermatitis on skin contact plus sunlight, and diseased roots at high concentration damaged internal organs shielded from UV. — published toxicology of Pastinaca sativa furanocoumarins, collected in a 2026 review Evidence D source
  Skin redness and blistering after sap contact and sun exposure; damage reported in liver, forestomach and esophagus with diseased parsnip; wounding raises furanocoumarin synthesis up to threefold in the damaged leaflets

What people believe that the data does not support

• No regulator has approved a health claim for parsnip itself, but the folate it carries has nine authorized claims in the EU, including one about maternal tissue growth in pregnancy. — EU Register on nutrition and health claims, snapshot of 21 September 2026, and 21 CFR part 101 (n = 9 folate entries) Evidence E source
  Zero entries under the name parsnips in the EU register and in 21 CFR 101; folate 9 authorized and 1 non-authorized; dietary fiber 6 authorized and 41 non-authorized, all of them for named fiber sources rather than vegetables

Who this works differently for

• A woman with delayed-type allergy to root vegetables patch-tested positive to celeriac, parsnip and carrot together, in the first reported case of systemic contact dermatitis from these foods. — one adult woman with systemic allergic dermatitis, prick and patch tested with fresh vegetables and selected allergens (n = 1) Evidence D source
  Contact sensitivity to celeriac, parsnip and carrot; negative to falcarinol, so the shared polyacetylene was not the culprit
• Infants weaned at six months who got nine days of zucchini, parsnip and sweet potato later ate more of a brand new vegetable than infants given only carrot. — 60 parent-infant dyads in South Birmingham, split by weaning before or after 5.5 months, 9 days of either a single vegetable or a variety pack, then measured acceptance of pea puree (n = 60) Evidence C source
  Infants weaned at 6 months in the single taste group ate significantly less pea puree than the variety group; no main effect of exposure group overall

What is still unknown

• The 2026 review of parsnip states plainly that the toxicology of its furanocoumarins in humans, especially chronic low dose intake from food, is still not understood. — authors of the 2026 review of Pastinaca sativa Evidence D source
  No human dose standardization and no safety validation for parsnip-derived products; chronic low-dose dietary and occupational exposure unquantified

The bottom line

A whole parsnip is 100 g in US survey coding and a cup of cooked parsnip is 160 g, which is a coding convention rather than a weighed plate. On 160 g the USDA reference entry works out to roughly 34 percent of the Daily Value for folate and 30 percent for fiber. Fiber is the stable part of this root. Across eight USDA Foundation samples it averaged 5.351 g per 3.5 oz (100 g) with a spread of 26 percent, while iron averaged 0.5053 mg and ran from 0.302 to 1.38 mg, a spread of 213 percent, so any single iron number for parsnip is the mean of eight samples rather than a property of the vegetable. The US and UK tables, paired by product name, agree on folate and fiber within about a tenth and differ on vitamin C by 30 percent, 11.85 against 17 mg per 3.5 oz (100 g), which is the nutrient most sensitive to how long a root waited before analysis. A 2026 review reports 26.8 g of fiber and 1.3 g of fructans per 3.5 oz (100 g) of dry matter, and dry matter is a different basis from the fresh root, so that figure cannot be set beside the 5.351 g above. Boiling in a little water and draining keeps 70 percent of the vitamin C and 70 percent of the folate while minerals hold at 90 to 95 percent, by a USDA factor written in 1975 for root vegetables as a group. Fiber is missing from that table, so nobody knows what boiling does to it. Controlled post-harvest aging for 30 days raised total phenolics in a parsnip extract roughly tenfold, from 0.0089 to 0.0897 mg GAE per ml, which is an industrial process measured in an extract rather than a root in your cupboard, and the same study did not measure what aging does to furanocoumarins. In mice, an aged parsnip extract lowered lung TNF-alpha and IL-1beta after an irritant challenge at a dose the authors themselves translate to about 10 g of fresh parsnip for a 154 lb (70 kg) adult, a translation they derived from a 7 percent extraction yield rather than measured. Now the caution. Parsnip is dominated by furanocoumarins, which cause phytophotodermatitis: sap on skin plus sunlight brings redness and blistering. In animal work on diseased roots at high concentration the same compounds damaged liver, forestomach and esophagus, organs that sunlight never reaches, and wounding the plant can raise furanocoumarin synthesis up to threefold in the damaged leaflets. No human dose threshold exists for any of this, and the 2026 review that collected it says so plainly. The practical reading is that a sound root on a plate is one thing, while a damaged or fungus-struck root, and sap on bare arms in the garden, are another. Separately, six days of a controlled diet built on the parsnip family lowered CYP1A2 activity in 36 healthy adults, and CYP1A2 is the enzyme that clears caffeine and a list of medicines. The abstract does not name the vegetables in that diet, and neither trial measured an effect on any medicine. One woman with systemic allergic dermatitis patch-tested positive to celeriac, parsnip and carrot together and negative to falcarinol. That is a single case, and it is the only signal here that the carrot family cross-reacts. Among 60 parent-infant pairs, babies weaned at six months who were given nine days of zucchini, parsnip and sweet potato later ate more pea puree than those given carrot alone, with parsnip one of three vegetables and its own share not separated out. No regulator has approved a health claim for parsnip itself. The folate in it carries nine authorized claims in the EU, one of them about maternal tissue growth in pregnancy, while every authorized fiber claim names a specific source such as oat, barley, rye, beet or wheat bran, and none of them covers vegetable fiber.

Compared with other foods

Sources

1. psnp-daily-r3-01 · food composition dataset
   Parsnips, raw Iron, Fe 0.5053 MG range 0.302–1.38 (median 0.3968), samples 8, spread 213%
   USDA FoodData Central, Foundation Foods, release 2026-04-30, FDC 2747659 · checked 2026-09-25
2. psnp-daily-r3-02 · food composition datasets
   vitamin C USDA 11.85 / CoFID 17 mg difference 30% ← DISCREPANCY
   USDA FoodData Central Foundation Foods FDC 2747659 and CoFID 2021, Public Health England, OGL v3.0, code 13-312 · checked 2026-09-25
3. psnp-daily-r3-03 · review of compositional data
   Research have shown that the root encompasses 21 g/100 g organic matter, 26.8 g/100 g dry matter (DM) dietary fiber, 1.3 g/100 g DM fructans and 5.9 g/100 g DM crude proteins resulting in low calorie content, i.e., 47 kcal/100 g.
   Food Science & Nutrition, 2026 · checked 2026-09-25
4. psnp-daily-r3-11 · dietary survey portion dataset
   1 cup 160 g
   USDA FNDDS, FDC 2709955 · checked 2026-09-25
5. psnp-daily-r3-07 · controlled feeding trial
   Using a randomized crossover design, we examined the effect of various vegetable diets on cytochrome P450 (CYP) 1A2, N-acetyltransferase 2 (NAT2) and xanthine oxidase activity in humans. ... Mean CYP1A2 activity for 19 men and 17 women (least squares means adjusted for sex, GSTM1 genotype, urine volume and feeding period) with basal, brassica, allium and apiaceous vegetable diets differed significantly (P </=ISOdia</= 0. 0005) by diet, irrespective of the caffeine metabolite molar ratio used to describe CYP1A2 activity; brassica vegetables increased (P <0.04) and apiaceous vegetables decreased (P </=ISOdia</= 0.02) activity compared with the basal and allium diets.
   Carcinogenesis, 2000 · checked 2026-09-25
6. psnp-daily-r3-08 · randomized crossover meal trial
   In a randomized crossover design, 25 participants underwent four phases with four different test meals at the end of each phase. ... The Api meal was not as effective in altering xenobiotic metabolites. Api primarily elevated mannitol/sorbitol.
   Food Res Int, 2025 · checked 2026-09-25
7. psnp-daily-r3-04 · nutrient retention factor table
   vitamin_c_mg 70% 30%
   USDA Table of Nutrient Retention Factors, Release 6 (2007), Retn_Code 3454 · checked 2026-09-25
8. psnp-daily-r3-05 · laboratory processing experiment
   The results were as follows: red ginseng exhibited a phenolic content of 0.0522 ± 0.008 mg/ml GAE, raw parsnip showed 0.0089 ± 0.004 mg/ml GAE, AP 10D had 0.0449 ± 0.003 mg/ml GAE, AP 20D demonstrated 0.0849 ± 0.002 mg/ml GAE, and AP 30D revealed the highest phenolic content at 0.0897 ± 0.003 mg/ml GAE.
   Frontiers in Nutrition, 2024 · checked 2026-09-25
9. psnp-daily-r3-06 · animal study
   Given that our extraction process for aged parsnip achieved a yield of approximately 7% based on fresh parsnip weight, the dosage we provided to the mice (i.e., 10 mg extract/kg body weight) translates to an equivalent dosage for an adult weighing 70 kg as the consumption of about 10 grams of fresh parsnip (16). With this exposure level, we demonstrated that both TNF-α and IL-1β mRNA expressions were decreased in the AP 20D intervention group, compared to the POS (p < 0.001 and p < 0.05, respectively; Figure 5A).
   Frontiers in Nutrition, 2024 · checked 2026-09-25
10. psnp-daily-r3-09 · toxicology review
    Furanocoumarins also have the potential to induce phytophotodermatitis in both humans and livestock. ... The findings presented here underscore that diseased parsnip, when present in significant concentration, can exert toxic impacts on internal tissues that are shielded from external sources of UV radiation.
    Food Science & Nutrition, 2026 · checked 2026-09-25
11. psnp-daily-r3-13 · regulatory register
    POL-HC-6370 Folate Folate contributes to maternal tissue growth during pregnancy Authorised
    EU Register on nutrition and health claims, claim POL-HC-6370, snapshot 2026-09-21 · checked 2026-09-25
12. psnp-daily-r3-10 · case report
    The patient was contact-sensitive to celeriac, parsnip, and carrot, but tested negative to falcarinol.
    Contact Dermatitis, 2014 · checked 2026-09-25
13. psnp-daily-r3-12 · controlled feeding comparison
    During the exposure period half of each age group was given carrot every day, and the other half was given a variety pack of courgette, parsnip and sweet potato. ... In particular, infants weaned at 6 months in the single taste group ate significantly less pea puree than those in the variety group.
    Appetite, 2014 · checked 2026-09-25
14. psnp-daily-r3-14 · review
    However, significant gaps remain in understanding the precise toxicological effects of these compounds in humans, particularly regarding chronic low‐dose exposure through diet or occupational contact. There is also a critical need for dose standardization and rigorous safety validation to ensure that potential health benefits of parsnip‐derived products can be harnessed without unintended toxic risks.
    Food Science & Nutrition, 2026 · checked 2026-09-25